The present invention relates to a method for actively influencing the intake noise of an internal combustion engine, wherein a correcting noise is generated which is superimposed on the intake noise. The invention also relates to an apparatus especially adapted to carry out the method of the invention.
The process of actively influencing the intake noise of an internal combustion engine, such as with a loudspeaker, is known. A possible circuit arrangement with a corresponding electrical process is illustrated in U.S. Pat. No. 5,321,759. The only feature of the arrangement of FIG. 1 of this document which is relevant in the present context is the intake tract 12, which emits an intake noise 20. The control system receives at least one engine speed signal 44 from the internal combustion engine 10, which is processed in the electronic control system 26. Additional variables, such as the position 18 of a throttle valve 16, can also be incorporated into the computing process of the electronic control system.
Using these measured variables, the control system 26 calculates an output signal, which is converted by a loudspeaker 28 into a sound, which is superimposed on the intake noise. The purpose of this measure is to reduce the intake noise. This purpose is achieved by taking advantage of the fact that a broad spectrum of the intake noise emanating from the internal combustion engine is directly dependent on the engine speed, while the frequency of the noise is based on various multiples of the engine speed. By emission of the noise determined in the intake tract by the control system through the loudspeaker 28, the corresponding partial noise in the intake tube can be reduced. In the ideal case, therefore, the noise emitted by the loudspeaker 28 requires an opposite and equal amplitude, so as to cancel the corresponding noise component.
To be able to measure the degree of noise reduction, an error microphone 30 is installed in the intake tract which absorbs the intake noise affected by the loudspeaker 28. The correspondingly filtered signal of the error microphone 30 provides the control system with information on the degree of noise reduction in the intake tract, so that the output signal for the loudspeaker 28 can be varied in terms of optimized noise reduction.
The system described above can be used to achieve effective reduction of the intake noise irrespective of the engine speed of the internal combustion engine. In comparison to conventional silencers, such as resonators, no additional volume is needed for active noise minimization. However, effective noise minimization using the method described above is not considered desirable in all operating states of an internal combustion engine. In certain operating states, the driver needs the acoustic information coming from the internal combustion engine for such purposes as to select the correct point at which to change gears during engine operation. Consequently, a consistent minimization of the intake noise across the entire engine speed range of the internal combustion engine would provide the driver with an inaccurate picture of engine characteristics, resulting in improper loading of the internal combustion engine and therefore in increased fuel consumption.
Furthermore, the publication xe2x80x9cAdjusting the Tonal Quality of Engine Noise Using Active Noise Control Techniquesxe2x80x9d (XP 000163374 ISSN:0374-4353) discloses a method for actively influencing the intake noise of an internal combustion engine. This method makes it possible to tailor the intake noise which remains after noise cancellation to a reference noise. In this way the intake noise can be transformed either into a more powerful sound or also into a very quiet noise. For this purpose an LMS (leased mean squares) adaptive filter is utilized which generates a starting signal phase shifted by 180xc2x0 in order to damp the intake noise. This starting signal is transformed into an analog signal which can be used to activate a loudspeaker arranged in the intake system. The acoustic waves generated by the loudspeaker are superimposed on the intake noise of the internal combustion engine, so that a cancellation is achieved. A microphone collects the instantaneous noise which remains after the cancellation and generates a corresponding feedback signal.
The filter input signal x(n) is read from a table depending on the angular position of the crankshaft. The values stored in the table list the harmonic oscillations of the intake noise which are to be canceled. These have the following form:
x(n)=A sin(aq)+B sin(bq)+C sin(cq)+ . . .
wherein
A,B,C, . . . are the relative magnitudes;
a,b,c, . . . are the generated oscillations; and
q is the angular position of the crankshaft.
To achieve a targeted adjustment of the intake noise of the internal combustion engine, a second generated signal d(n) is required, which is based on the angle of the crankshaft. This second signal forms the reference noise, which should remain after noise cancellation. The values for the reference noise have the following form:
d(n)=Axe2x80x2 sin(axe2x80x2q)+Bxe2x80x2 sin(bxe2x80x2q)+Cxe2x80x2 sin(cxe2x80x2q)+ . . .
wherein
Axe2x80x2, Bxe2x80x2, Cxe2x80x2 . . . are the desired relative magnitudes;
axe2x80x2, bxe2x80x2, cxe2x80x2 . . . are the desired oscillations or vibrations; and
q is the angle of the crankshaft.
The error signal e(n), which is utilized to correct the coefficients of the LMS-adaptive filter, is generated by subtraction of the feedback signal of the microphone from the reference signal of the reference noise d(n). In this way the signal y(n) emitted from the LMS adaptive filter will assure that the intake noise emitted by the internal combustion engine will be matched or tailored to the reference noise. The reference noise can be maintained over the entire speed range of the internal combustion engine. Inlet or outlet noise vibrations, which are not created by the internal combustion engine, are generated by the active noise control system only depending on the angular position of the crankshaft.
In the described system a constant tailored adaptation of the reference noise depending on the angular position of the crankshaft is achieved. This tailored adaptation has the result that the reference noise is based exclusively on the crankshaft and other influences are not taken into account.
One could deactivate active noise minimization in certain operating states. However, this would result in an abrupt change in the intake noise, which would similarly confuse the driver, as he is not accustomed to such changes in conventional internal combustion engines. Consequently, the problem described above cannot be satisfactorily solved in this manner.
Therefore, it is the object of the invention to provide a method and/or apparatus for carrying out this method which makes possible better matching or tailoring of the intake noise.
This and other objects are achieved by the method of the invention as described and claimed hereinafter, as well as by the apparatus for carrying out the method, which apparatus is also described and claimed hereinafter.
In the method of the invention, an electromechanical converter or transducer which may, for example, comprise a loudspeaker which generates a correcting noise, is provided in a manner known in the art. This converter is installed in such a way that a correcting noise generated by the transducer can be superimposed on the intake noise. This can, for example, be achieved by securing the loudspeaker to the outside wall of the intake tract so that it emits sound into the interior of the intake duct. However, it is also possible to install the loudspeaker outside the intake system in the engine space. The key element here is that the sound waves emitted by the loudspeaker can be superimposed on the intake noise.
In addition, a sensor, especially a microphone, is provided which is installed in the engine space or in the intake tract in such a way that it can register the actual noise resulting from superimposition of the correcting noise from the electromagnetic converter on intake noise of the internal combustion engine. Both the electromechanical converter and the sensor are connected to the control system which, furthermore, processes at least one engine speed signal stemming from the internal combustion engine. The frequency, amplitude and phase of the output signal which drives the electromechanical converter are modified in dependence on the engine speed signal and the signal from the sensor.
The engine speed signal can be generated by a sensor provided specifically for this purpose and connected to the control system. Alternatively, it is also possible to obtain the engine speed signal from another information circuit provided in the internal combustion engine. Modern internal combustion engines feature an engine management system which also ensures utilization of the engine speed signal. This system can be utilized to obtain the engine speed information, thus eliminating the need for an additional engine speed sensor.
The electromechanical converter can be constructed in the form of a suitably dimensioned loudspeaker. If the overall system is skillfully designed, this can, for example, be a commercially available loudspeaker with a 15 cm diameter which is secured to the raw air line. The control sensor can be a simple electret microphone, which is especially effective if it is installed in proximity to the intake opening of the intake system. The electronic control system preferably comprises a signal processor system in which the functional units of the control system are digitally replicated. This allows for a very small, integrated and cost-effective construction of the system. Of course, the signal process system can also be accomplished with an analog computer circuit.
According to the invention, the method provides that the actual noise, which results from the superimposition of the correcting noise on the intake noise, is compared with a reference noise. It should be emphasized that the purpose of the reference noise is to achieve a desired noise at the intake tract of the internal combustion engine, meaning that it can also differ from zero. By comparing the actual noise with the reference noise, the control system can modify the characteristics of the correcting noise so that it approximates the desired reference noise when it is superimposed on the intake noise of the internal combustion engine. These approximation steps are constantly repeated, or the intake noise is even continuously adjusted additionally to conform to the reference noise.
This means that the desired reference noise must somehow be made available to the control system. It can, in particular, be determined in dependence on the engine speed of the internal combustion engine. This is advantageous because, for the reasons discussed earlier, the intake noise is also primarily dependent on the engine speed. This enables an intake noise to be generated as an actual noise. The objective can be to reduce the intake noise or, in certain cases, to increase the intake noise. Whether a reduction or an increase is achieved depends on the phase position of the correcting noise relative to the intake noise. The amount of the increase or reduction of the intake noise can be influenced by the amplitude of the correcting noise, and is limited by the loudspeaker output. The frequency of the correcting noise is directly dependent on the engine speed of the internal combustion engine.
The comparison of the actual noise with a desired reference noise can be advantageously utilized in various ways. For example, if the output of the loudspeaker is insufficient to cancel a strong intake noise, it can be transformed into a moderate intake noise tolerable in terms of human perception. In addition, the driver of the vehicle requires acoustic feedback from the engine at certain operating intervals. This is necessary, for example, to determine the correct point for changing gears. In these operating states, the intake noise of the internal combustion engine can be influenced directly, e.g., by a decreasing intake noise reduction in higher engine speed ranges. Finally, by specifying the reference noise, the intake noise can be influenced to achieve a sporty sound. This allows for application scenarios in the area of so-called sound design.
An apparatus for carrying out the method of the invention is also described hereinafter. This apparatus must comprise at least the following components:
A control system is necessary which can process the engine speed signal D of the internal combustion engine in order to generate a control signal A based on the engine speed. The control signal A is used to actuate the electromechanical converter, especially the loudspeaker used to generate the correcting noise. In addition, the control system must receive information about the reference noise signal S and the actual noise signal I. The reference noise signal is used by the control system for comparison with the actual noise signal, so that the variance can be determined. The actual noise signal is comprised of the superimposition of the correcting noise over the intake noise, as described earlier. The reference noise signal corresponds to a reference noise which is to be generated by influencing the intake noise with the correcting noise.
To generate the engine speed signal, the engine speed of the internal combustion engine must be supplied to the control system through an interface. An engine speed sensor, which can also be integrated into the engine management system, is generally connected to this interface. In most cases, this type of sensor already provides an engine speed signal, which may have to be converted into the engine speed signal D.
A sensor must also be provided to sense or register the actual noise. This sensor then provides a corresponding actual noise signal I, which can be processed in the control system.
Finally, an electromechanical converter must be provided to generate the correcting noise. A commercially available loudspeaker is generally sufficient for this purpose.
The described device requires a minimal use of components to actively influence the intake noise. The control system preferably comprises a digital computer. Accordingly, the signals must be converted into analog or digital form. It may be necessary to amplify the control signal to achieve the desired amplitudes of loudspeaker vibrations needed to generate the correcting noise.
In accordance with one specific embodiment of the control system, the apparatus comprises the following components:
A first means is provided to generate the control signal, whose frequency is dependent on the engine speed signal D. This may, for example, be a generator for a sinusoidal control signal.
A second means is used to set the level and phase of the control signal A in dependence on a comparison signal V. The comparison signal V represents the outcome of the comparison between the actual noise signal I and the reference noise signal S. Therefore, it indicates the divergence of the actual noise from the desired reference noise. Based on this value, the level and phase of the control signal is corrected, resulting in further approximation of the actual noise to the reference noise. A supplementary means to account for the acoustic transfer function between the converter and the sensor can be useful in this process. This allows for the free choice of installation locations for the electromechanical converter and sensor. Thus, the transfer function is a constant parameter dependent on the system.
A third means is provided for generating the reference noise signal S. This means can also be integrated into the control system""s computer. The minimum input variable processed by the computer is the engine speed signal D, which can be used to generate a reference noise signal S which is dependent on the engine speed. Of course, other engine parameters can be incorporated into this calculation, such as the position of the gas pedal, the selected gear in the transmission, or the throttle valve mentioned earlier.
A fourth means is provided to form a comparison signal from the actual noise signal and the reference noise signal. This is preferably achieved by forming the difference between the two signals, which permits conclusions to be drawn on the variance between the actual and reference noises. This results in the comparison signal V, which is used to influence the control signal A.
As mentioned earlier, it is especially advisable to execute the control signals in sinusoidal form. They can then be adjusted to conform to the higher orders of the engine speed-dependent engine noise. If several orders of the engine noise are to be influenced, the device must be cascaded. This means that the first and second means of the control system are arranged in multiple parallel arrays in the control system. Each parallel array is responsible for the generation of a special control signal A and/or for the adjustment of its level and phase. A fifth means then groups the control signals for addition, so that their superimposition on the third means can be passed on to generate the reference noise signal. This makes it possible to trigger the electromechanical converter.